Anecdotal evidence means nothing. Just because someone else (or many someone elses) goes naked without a scratch means nothing regarding whether or not you'll get a scratch going naked. You need to determine what precautions you're willing to take to avoid scratches. Polling others isn't the way to determine that. No percentage of naked users is a guarantee that you won't get a scratch.
Research via the countless screen protector threads here and see if one sounds like it would suit you.
Always consider the source. The iPad screen certainly can be scratched by many more materials than just diamonds. Searching around would quickly verify that as not everyone with a scratch has one due to a diamond.
Either you lack imagination or you're unaware that there are screen protectors that won't degrade image quality.
Scratching the glass is hard, scratching the oleophobic coating is easy. I let my sister use my iPad 1 for a few minutes and bam scratches on the screen from her fingernails.
I've never been without a screen protector since. I currently have an anti fingerprint one on my iPad 3 that works a treat and feels nice and silky. (It's also crystal clear)
But they are degrading how ipad feels in touch.
Ive put screen protector on mine iPad screen but took it out after one day. I couldnt stand that it doesnt feel so smooth and sexy anymore (but to be honest it is packed into case and sleeve, so ive shouldnt hurt it by accident)
The screen is very difficult to scratch. You would almost have to be trying to scratch it. Sure, there will be someone who will claim that a scratch came out of nowhere, but I have never babied the screen on all 3 iPads I've owned. I have used the smart cover since day one and have cleaned my screen with my shirt and any towel around and never had a single scratch. I have dozens of friends with them and I'm not aware of a single person with a scratch.